This invention relates to an improvement in laser of the type of metal vapor discharge laser.
In recent years, many gas laser tubes, many have been made with the coaxial construction of a laser capillary, a cathode and an enclosure. For instance, helium-neon laser tubes generally adopt such coaxial construction. This is because the coaxial construction allows the laser tube to be made compact and suitable for automatic manufacturing with a high precision.
However, in the conventional coaxial structure metal-vapor gas laser of FIG. 1, wherein lasing is excited by means of discharge in the metal gas, its life is shortened because of sputtering of cathode material around the cathode caused by bombardment of cathode by metal ions in the discharge plasma.
In FIG. 1 which shows one example of the conventional coaxial structure type metal-vapor laser tube, in a glass envelope 170, a laser capillary 121 is disposed on the axis of the envelope 170. A cylindrical cathode 102 is disposed coaxially with and surrounding the laser capillary 121. Between an anode 101 and one end of the laser capillary 121, a reservoir 122 containing a specified amount of metal 131 such as cadmium is connected, in a coaxial relation with the lasing capillary 121. The other end of the laser capillary 121 is supported by one end of a supporting tube 115 which is made of glass and air-tightly connected to the envelope 170. The insertion of the laser capillary 121 in the supporting tube 115 is of normal lax fitting of USAS. At the other end of the supporting tube 115 and at the narrowed end of the envelope 170 containing the anode 101 are provided a pair of known Brewster windows 112 and 111, light passing windows with oblique glass plate, respectively. A discharge passing hole 105 is formed on the supporting tube 115 in a manner to face a part of inside surface of the cathode 102.
Operation, namely lasing of this laser is made by impressing a D.C. voltage across the anode 101 and the cathode 102 and disposing this lasing tube in a known external lasing cavity which comprises a pair of lasing mirrors to be disposed facing both Brewster windows 112 and 111.
The reservoir 122 contains the metal 131 which becomes an laser active medium. When the reservoir 122 is heated, the metal 131 is evaporated and, by means of cataphoresis effect of a discharging, the metal vapor becomes evenly distributed with a specified vapor pressure in the laser capillary 121. The discharge plasma which passes through the laser capillary 121 is led, through the discharge passing hole 105, onto the inside surface of the cold cathode 102 and makes recombination on the inside surface of the cold cathode 102. The metal vapor formed by the recombination is trapped on a part or parts of relatively low temperature of inside face of the envelope 170, thereby forming a vapor-deposited metal film 132 thereon. Hereupon, the discharging plasma led onto the inside surface of the cold cathode 102 contains ions of considerably large momentums. For instance, in a cadmium ion laser utilizing helium gas as the carrier, the discharge plasma contains a considerable amount of cadmium ions. These cadmium ions impact the surface of cold cathode 102 and cause sputtering of cathode material around the cathode. As a result, a deposit layer due to sputtering is formed on the inside surface of envelope 170 at the portion around the cathode 102. The layer of deposit undesirably absorbs the carrier gas, thereby reducing pressure of the carrier gas and causing the life of the tube to decrease.